In plants photosynthetically fixed carbon is ultimately converted into two main carbohydrate products, sucrose and starch. Sucrose is the form in which most fixed carbon is exported from the photosynthetic cell. Sucrose is then translocated to various parts of the plant which have a need for this sugar such as regions of active growth and developing seeds or tubers. Sucrose is synthesized in the cytoplasm of photosynthetic cells from the precursor dihydroxyacetone phosphate (DiHOAcP). In the last two steps of sucrose biosynthesis UDP-glucose is converted to sucrose by the successive action of sucrose phosphate synthase (SPS) (E.C. 2.4.1.14) and sucrose phosphatase. By modulating the level of SPS in plants it may be possible to control carbon partitioning in photosynthetic cells. Accordingly, the availability of nucleic acid sequences encoding all or a portion of a sucrose phosphate synthase protein would facilitate studies to better understand carbon partitioning in plants.
Worrell, A. C. et al. ((1991) Plant Cell 3:1121–1130) describe a maize cDNA that encodes a sucrose phosphate synthase as confirmed by the ability of the cloned sequence to direct sucrose phosphate synthesis in E. coli. Additional nucleic acid fragments encoding sucrose phosphate synthase have been isolated by other groups (e.g., U.S. Pat. No. 5,665,892; JP 2000262283).